In conventional axial compressors, inlet struts of the type mentioned above extend exclusively radially, i.e., parallel to a normal plane of the longitudinal axis of the inlet connection piece, so that the center of the first, or front, bearing is arranged axially in the flow direction of a fluid to be compressed substantially level with the area center of this front cross section; in other words, the bearing is arranged axially in the center of the inlet strut below the point where it merges with the inlet housing.
In the present context, the center of the bearing refers in particular to a piercing point of a bearing axis through a plane of symmetry of a symmetrical bearing, a center of mass of the bearing, the geometric center between the axial end faces of the bearing, or a pressure point of the bearing.
Since the inlet struts are often connected to the inlet housing relatively far axially in front toward the inlet cross section of the inlet connection piece, particularly for purposes of robustness and for reasons pertaining to manufacture, in order to find support, for example, against corresponding reinforcements of the inlet housing or, when cast, to prevent sharp variations in wall thickness, the first, or front, bearing is also arranged correspondingly far to the front resulting in a relatively large distance between this bearing and a second, rear bearing of the rotor of the axial compressor which is arranged behind the first bearing in the flow direction.
One or more fluid passages can be formed in the inlet struts. Fluid passages of this kind can be used, for example, for lubrication of the bearing and, to this end, open into the bearing housing in, or in the vicinity of, the bearing on one side and are connected to a lubricant supply or lubricant discharge outside the inlet housing on the other side, for example, by means of lubricating nipples, lines, passages in adjoining housing parts, or the like.
Fluid passages of this kind formerly extended substantially radially in order to minimize the length of the fluid passage and, therefore, to minimize weakness in the inlet strut supporting the bearing housing and the cost for producing them, which was generally carried out by cutting.
As a result, a bearing supplied by the radial fluid passage must be arranged axially at the height of the outlet opening of the fluid passage exiting from the inlet housing, which likewise disadvantageously increases the center-to-center distance between the bearings of the rotor. However, a greater center-to-center bearing distance can negatively influence the rotor dynamics.